By determination of the rheological flow curve of minute quantities of axoplasm drawn into a microcapillary tube connected to a high vacuum, extruded axoplasm was shown to behave as a pseudoplastic fluid with a viscosity of 106-times that of water and without significant signs of time-dependent thixotropic or viscoelastic properties. A theoretical analysis of peristaltic pumping of such pseudoplastic fluids by sinusoidal surface waves was combined with experimental studies of a mechanical model designed to simulate peristaltic drive. The correlation of the respective data permitted quantitative predictions for the peristaltic mechanism of axonal flow, with speed being a function of peristaltic wave geometry and fluid properties, yielding a theoretical mean value of 0.45 mm/day, i.e., of the same order as that observed in the living nerve fiber.Axonal flow "refers to the fact that the 'axis cylinder' of the mature neuron keeps growing forth throughout life from its base in the cell body, its macromolecular substance being .... conveyed as a cohesive semisolid mass (18) toward the distal ending .... at a standard rate of the order of 1 mm per day, driven by a microperistaltic wave generated in the axonal surface" (1). Time-lapse motion pictures of live nerve fibers have recorded that wave (2), and the studies reported here are an attempt to define its properties and drive in physical terms. Thixotropic. A fluid that decreases in viscosity with fixed rates of shear as time increases, and has a tendency to take a set when at rest.

This paper reports upon an experimental investigation in which a heat-transfer instrument was designed, built, and applied in a rarefaction wave tube. An analysis of the heat-transfer instrument was made to evaluate the significant parameters which influence the instrument performance in the measurement of transient heat flux between the gas and wall. A mathematical analysis based upon the heat balance integral procedure, considering variable density and time-dependent free stream gas temperature, was performed to interpret the gas-to-end-wall heat transfer in a rarefaction wave tube. The heat-transfer rates predicted by the analysis com pared favorably with values measured by the calorimeter type thermistor heat-transfer instrument.

If a gas is permitted to expand freely from a vessel of constant volume, the gas remaining in the vessel is generally considered to undergo reversible adiabatic expansion. For such a case, the theoretical backgrounds are developed from the points of view of thermodynamics and gas dynamics. Experiments are reported in which it is shown that, for expansions occurring over short time intervals, the temperature changes are essentially those predicted for reversible adiabatics. Some speculations are offered as to the mechanisms obtaining in the slower expansions.

Experiments were conducted on the effects of the shift of the gas mass from the high-pressure to the low-pressure sides of a divided vessel, with communication by (a) bursting diaphragm and (b) bypass valve. Analytical solutions indicate the true complexity of the problem and the need for transient force and pressure information.